Technological Field
The present invention relates to a facsimile communication device, a line disconnection judgment method and a non-transitory recording medium storing a computer readable program which can detect the open (disconnection) of the line, which is caused in the facsimile device of the opposite side, during the facsimile communication.
Description of the Related Art
As a social infrastructure used in the facsimile (FAX) communication, the environment (digital lines) in which the network is interposed by IP-PBX (Internet Protocol Private Branch eXchange), various types of Network-Gateway devices, TA (Terminal Adapter) and the like in the middle of the paths, is increased. In the FAX communication (VoIP (Voice over Internet Protocol) communication/FoIP (Fax over Internet Protocol communication) using the above-described lines, many line disturbances are caused and the communication errors are extremely increased. Therefore, it is requested to specifically grasp the cause of the communication error and the timing at which the disturbance is caused.
As the specific case thereof, mainly in case that the line is disconnected when the receiver detects the abnormality, because the transmitter does not immediately recognize the disconnection of the line, which is caused in the receiver, there are some cases in which the transmitter continues to capture the line for up to several minutes since the receiver disconnects the line. Therefore, the transmitter cannot immediately disconnect the line.
As the facsimile communication device for solving the above problem, the following facsimile communication device is disclosed in Japanese Patent Application Publication No. H09-149226. In this facsimile communication device, the communication method in which the flag sequence is transmitted to the transmitter from the receiver during the transmission of the image data, is adopted. When the flag sequence transmitted from the receiver is lost, the transmitter detects the abnormality caused in the receiver.
Further, as the communication environment of the facsimile communication, the IP telephone network in which the network is interposed by the exchanges, such as IP-PBX (Internet Protocol Private Branch eXchange), various types of Network-Gateway devices, TA (Terminal Adapter) and the like, has been increased. In the IP telephone network, there are many cases in which the signals are processed by the exchanges. FIG. 25 shows the part in which the sound data is processed in the IP telephone network. FIG. 26 shows the delay in the signal transmission in the IP telephone network.
As a specific case in which the signal is processed, it is generally known that when the exchangers (TA/PBX/GW) which are provided in the middle of the paths detect the FAX signal (FAX terminal identification tone of the transmitter side: CNG; FAX terminal identification tone of the receiver side: CED/ANSam), the operation mode of each exchanger is switched, such as the sound data is transmitted after the sound data is accumlated in the buffer. It is confirmed that the delay in the signal or the lack of the signal is caused (the silence section is caused) due to the switch of the mode and the communication error is caused.
In the facsimile communication, the mechanism for causing the communication error due to the delay in the signal or the lack of the signal will be explained as compared with the normal case in which the delay in the signal or the lack of the signal is not caused.
FIG. 27 shows the normal communication procedure (communication sequence). In this procedure, the phase B which is the phase after the communication is established, will be explained. The receiver transmits the receiver capacity information (CSI (Called Subscriber Identification)/DIS) indicating the capacity of the receiver (the resolution, the size of the original, the maximum communication speed and the like) to the transmitter.
The transmitter which receives the receiver capacity information, determines the communication mode, such as the resolution and the like, in accordance with the transmission condition which is set to the transmitter (the communication speed, the resolution and the like), the capacity of the receiver, which is recognized from the receiver capacity information, and the like. Then, the transmitter transmits the capacity confirmation information (TSI (Transmitting Subscriber Identification)/DCS (Digital Command Signal)) indicating the determined communication mode to the receiver. Further, the transmitter transmits the training signal (TCF) for confirming the condition of the communication line, to the receiver.
The signals which are transmitted from the receiver to the transmitter and the signals which are transmitted from the transmitter to the receiver are delayed to a certain degree while the signals are transmitted via the communication line, and reach the facsimile device of the opposite side.
The receiver confirms the condition of the communication line by receiving the training signal. When the receiver recognizes the finish of the transmission of the training signal, the receiver transmits the training result to the transmitter. For example, in case that the receiver normally receives the training signal and finishes the preparation for receiving the data, the receiver transmits the CFR (Confirmation To Receive) signal as the training result. On the other hand, the receiver fails in the training, the receiver transmits the FTT signal.
In case that the transmitter receives the CFR signal as the training result from the receiver before the predetermined retransmission interval (3 seconds) elapses since the transmission of the training signal is finished, the transmitter finishes the phase B and transfers to the phase C to transmit the image data.
FIG. 28 shows an example of the case in which the transmitter cannot receive the training result from the receiver before the retransmission interval elapses. In FIG. 28, the delay caused in the communication line is more than that of FIG. 27. Therefore, the training result (CFR) transmitted from the receiver to the transmitter reaches the transmitter after the retransmission interval (3 seconds) elapses since the transmitter finishes the transmission of the training signal. Because the transmitter cannot receive the training result from the receiver before the retransmission interval elapses (because the silence section in which the intended signal is not received from the receiver is caused), the transmitter retransmits the capacity confirmation information (TSI/DCS) and the training signal (TCF). Because the CFR signal transmitted from the receiver reaches the transmitter when the transmitter retransmits the capacity confirmation information and the training signal, the transmitter cannot receive the CFR signal. As a result, the communication error is caused.
In FIG. 29, because the capacity confirmation information (TSI/DCS) and the training signal (TCF) which are transmitted from the transmitter are lacked in the IP telephone network, the silence section which exceeds the retransmission interval for the receiver capacity information (CSI/DIS signal) is caused in the receiver. As a result, the receiver retransmits the receiver capacity information (CSI/DIS signal) to the transmitter. Because the transmitter cannot receive the training result from the receiver before the retransmission interval elapses (because the silence section which exceeds the retransmission interval is caused), the transmitter retransmits the capacity confirmation information (TSI/DCS) and the training signal (TCF). In the transmitter, the retransmitted capacity confirmation information collides with the receiver capacity information (CSI/DIS signal) which is retransmitted by the receiver. Therefore, the transmitter cannot identify the receiver capacity information (CSI/DIS signal). Further, in also the receiver, the collision between the signals is caused. Therefore, the receiver cannot identify the capacity confirmation information (TSI/DCS) and the training signal (TCF) which are retransmitted by the transmitter. As a result, the communication error is caused.
In case that the disturbance is caused due to the delay in the signal in the IP telephone network as described above, it is difficult to specify the cause of the disturbance by the analysis using the protocol trace or the analysis using the sound data obtained from only one of the transmitter and the receiver. Therefore, in general, the communication sound is recorded in each of the transmitter and the receiver when the disturbance is caused, and the cause of the disturbance is analyzed by actually listening to recorded sound data to compare them.
In Japanese Patent Application Publication No. 2007-174061, the following control method for stopping the facsimile communication is disclosed. In the facsimile communication using the IP telephone network, when the silence section is caused due to the increase in the traffic load of the provided exchangers, because the retransmission request is increased and communication time becomes long, the facsimile device is occupied by the communication process. In order to solve this trouble, in this control method, the silence section is detected by a filter circuit. When the number of the detected silence sections exceeds the predetermined number, the facsimile communication is stopped.
In the facsimile communication device disclosed in Japanese Patent Application Publication No. H09-149226, it is required to use the special standard (G3C system) different from G3-FAX standard (which is the ITU-T standard) which is a general facsimile communication standard. In the G3-FAX standard which is widely popularized, there is no protocol in which the flag sequence is transmitted from the receiver during the transmission of the image data. Therefore, the above problem cannot be solved by adopting the method disclosed in Japanese Patent Application Publication No. H09-149226.
Further, in the method for analyzing the cause of the disturbance by actually listening to and comparing the recorded data of the communication sound in each of the transmitter and the receiver when the disturbance is caused, an operator must listen to the long recorded data and the analysis work is increased.
In the method disclosed in Japanese Patent Application Publication No. 2007-174061, by stopping the communication, it is possible to temporarily release the unnecessary occupation of the facsimile device. However, it is not possible to contribute to the investigation into the cause of the disturbance.